In centrally controlled telecommunication switching systems, more particularly telephone switching systems, subscriber lines and/or interexchange trunks from or to switching centers are interconnected by switching elements (crosspoints) forming in their entirety a switching network in accordance with the connections desired in each case. The arrangement of the switching elements within the switching network likewise, is referred to as the trunking scheme of the latter.
Among the possible trunking schemes of telecommunication switching systems various types can be distinguished, e.g., switching networks with stage-by-stage call buildup, which are divided into several ranks of selectors and in which during (stage-by-stage) call buildup only the possible paths within the rank of selectors currently being reached are taken into account, or switching networks with conjugate selection in which for a call buildup always the busy/idle status of the whole switching network is taken into account.
In the case of switching networks with conjugate selection a distinction can be made between two types of switching networks. The first uses an elongated trunking scheme, in which on two sides of the switching network there are disposed two groups of terminals, and connections are possible only between one terminal of one side and one terminal of the other side. The second is a switching network using a reversed trunking scheme, in which all terminals are located on the same side of the switching network. Such switching networks with the reversed trunking scheme are disclosed, for example, in Reports on Telephone Engineering VI (1970) 1/2, published by Siemens A. G., Berlin and Munich, West Germany, pp. 28-33 and 65-73, (cf. British Pat. No. 1,058,893), have the advantage of practically full availability to the outgoing lines, a high flexibility with respect to different conditions of compatibility and a far-reaching modular structure.
With regard, however, to the individual components of prior art space-division switching networks with reversed trunking scheme and crosspoints formed by dry reed contacts in metal enclosures these cannot be made by the increasingly popular large-scale integration techniques. Difficulties are encountered in this form of construction with the so-called pin limitation, i.e., limitation in function by limitation in available pin space, excessive heating, and technological limits which possibly allow the placing of, e.g., a matrix with 4 . . . 16 crosspoints, on a single component in medium-scale integration.
It is an object of the invention to provide a form of construction for such networks exploiting the promising possibilities of large-scale integration for a switching network using the reversed trunking scheme, whereby several hundred switches can easily be placed on a single component.